Aluminum material surface treatment method, surface treatment apparatus, and treated surface aluminum material

ABSTRACT

A coating is formed by coating a treatment solution containing a 20-400 ppm total, calculated as titanium and calculated as zirconium, of a titanium fluoride compound and/or a zirconium fluoride compound on the surface of an aluminum material so that the total of titanium and zirconium is 4-25 mg/m2, and drying.

TECHNICAL FIELD

The present invention relates to a surface treatment method of an aluminum material with a treatment solution containing at least one kind of a titanium fluorine compound and a zirconium fluorine compound, a surface treatment apparatus for use in the surface treatment method, and a surface-treated aluminum material obtained by the surface treatment method and suitably for use in transportation equipment such as an automobile, a ship, and an airplane, particularly for use in an automobile panel.

BACKGROUND ART

Recently in the automobile industry, improvement of fuel economy resulting from weight reduction of members has been required from global environmental problems such as regulations on CO₂ emission. Aluminum materials have a light specific gravity which is about ⅓ of that of iron materials. For parts where the iron materials have been used, the aluminum materials are attracting attention as materials which can replace the iron materials due to requests for weight reduction. As for the aluminum materials, an Al—Mg alloy and an Al—Mg—Si alloy are used depending on their properties. In addition to a welding method such as brazing or a mechanical joining method such as caulking or riveting, a joining method by bonding is often used as a method for joining an aluminum material.

Bonding by a bonding agent is surface joining which is suitable for enhancing rigidity, and not only aluminum materials can be joined to each other, but an aluminum material can be also joined to a different material such as a different kind of metal or resin without any restriction. In addition, electric erosion can be prevented, and bonding can be achieved easily independently of thickness of a material to be bonded to or a place where the bonding is performed. However, a bonding portion bonded by the bonding agent may be degraded by intrusion of moisture, oxygen, chloride ions, or the like. Since bonding strength is reduced thereby, sufficient bond durability is required. In the background art, a surface treatment method in which a coating film is formed on a surface of an aluminum material with a treatment solution containing titanium and zirconium has been proposed as a technique for improving the bond durability of the aluminum material.

For example, Patent Literature 1 proposes a method for treating a metal material before applying a bonding agent thereto. The method for treating a metal material before applying a bonding agent thereto includes a step (I) of treating a to-be-treated material made of an aluminum-based substrate with a chemical treatment solution containing a zirconium fluorine complex and/or a titanium fluorine complex, and a step (II) of applying a surface treatment solution containing a hydrolytic polycondensate of a silane coupling agent.

Patent Literature 2 proposes a method for forming a chromium-free chemical conversion coating on a surface of an aluminum alloy by a non-rinsing method. In the method for forming a chromium-free chemical conversion coating in Patent Literature 2, a solution containing a predetermined organic coating film forming agent is brought into contact with a surface of an aluminum alloy, and after a contact time of 1 to 40 seconds, the solution on the surface is dried at a temperature of 50 to 125° C. without rinsing.

CITATION LIST Patent Literature

Patent Literature 1: JP-A-2006-152267

Patent Literature 2: JP-A-H09-511548

SUMMARY OF THE INVENTION Technical Problems

One of the methods for surface treatment of an aluminum material is a reaction type treatment in which a treatment solution is applied to an aluminum material to cause a reaction, followed by rinsing with water and drying to form a coating film. The reaction type treatment is performed by spraying the treatment solution onto the aluminum material or immersing the aluminum material into the treatment solution. Accordingly, an excess amount of the treatment solution is generally used. In addition, for the reaction type treatment, it is necessary to ensure a reaction time of the treatment solution before rinsing the aluminum material with water. Therefore, the use amount or waste amount of the treatment solution tends to increase, and it also takes much time for the treatment. There is a difficulty on productivity, environmental feasibility, or the like.

Even in the reaction type treatment, the use amount or waste amount of the treatment solution can be reduced by recovering the treatment solution used once and reusing it in the next treatment. However, when the treatment solution is applied onto an aluminum material, aluminum in the surface is etched to elute into the treatment solution. Thus, the aluminum concentration increases in the treatment solution. When the aluminum concentration in the treatment solution increases, increase of pH is prevented near the surface of the aluminum material. Thus, it is difficult to form a sufficient amount of the coating film. When the temperature of the treatment solution increases, the amount of the coating film can be improved without increasing the amount of the treatment solution. However, energy cost is required for increasing the temperature of the treatment solution.

Another surface treatment method of an aluminum material is a coating type treatment in which a treatment solution is applied onto an aluminum material, and a coating film is then formed without rinsing the aluminum material with water. In the coating type treatment, the use amount or waste amount of the treatment solution can be reduced, and the treatment time can be also shortened. In addition, the aluminum concentration in the treatment solution is hardly increased. It is therefore possible to reduce the energy cost or the environmental load. However, the coating film formed by the coating type treatment tends to decrease in bond durability as compared with a coating film formed by the reaction type treatment. When an aluminum material having a coating film formed by the coating type surface treatment and bonded with another material is left under a wet environment, the bonding strength deteriorates conspicuously. It is therefore desired to improve the bond durability.

The present invention has been therefore created to solve the aforementioned problems. An object of the invention is to provide a surface treatment method and a surface treatment apparatus, in which a coating film having excellent bond durability can be formed on a surface of an aluminum material in spite of reduction in energy cost and environmental load. Another object of the present invention is to provide a surface-treated aluminum material having excellent bond durability.

Solution to Problems

In order to solve the aforementioned problems, a surface treatment method of an aluminum material according to the present invention includes the steps of: applying a treatment solution containing at least one kind of a titanium fluoride compound and a zirconium fluoride compound to a surface of an aluminum material; and drying the treatment solution applied to the surface of the aluminum material, thereby forming a coating film, wherein, in the treatment solution to be applied to the surface of the aluminum material, a total of a concentration of the titanium fluoride compound in terms of titanium and a concentration of the zirconium fluoride compound in terms of zirconium is 20 to 400 ppm; and the treatment solution is applied to the surface of the aluminum material so that a total of titanium and zirconium is 4 to 25 mg/m².

According to the surface treatment method, since the titanium concentration and the zirconium concentration in the treatment solution are proper, unreacted fluorine compounds derived from the treatment solution containing the titanium fluoride compound, the zirconium fluoride compound, or the like do not remain when the treatment solution is dried. Thus, the amount of fluorine compounds distributed in the surface of the coating film is reduced. Due to the reduction in the amount of fluorine compounds, the coating film can exert excellent bond durability. In addition, since the surface treatment method is a coating type surface treatment method, the treatment solution which has reacted in the surface of the aluminum material or the coating film which has been formed on the surface does not have to be rinsed with water. Therefore, the treatment time of the surface treatment is shortened, and the quantity of waste liquid after rinsing the aluminum material with water is reduced. That is, the productivity or the environmental feasibility can be improved, and the energy cost can be also reduced. In addition, when the applied treatment solution is dried, 0 to 40% of the titanium fluoride compound or zirconium fluoride compound contained in the treatment solution is generally evaporated and lost. However, the treatment solution having the proper titanium concentration and the proper zirconium concentration is applied while adjusting the total amount of applied titanium and zirconium. Thus, the coating film formed by drying has a proper coating amount. Therefore, there is no fear that the coating amount is so small as to lose corrosion resistance or adhesion to a bonding agent, or there is no fear that the coating amount is so large as to make the coating film fragile. Combined with the reduction of fluorine compounds, the coating film can exert excellent bond durability

A surface treatment apparatus of an aluminum material according to the present invention includes: an application unit that applies a treatment solution containing at least one kind of a titanium fluoride compound and a zirconium fluoride compound to a surface of an aluminum material; and a drying unit that dries the treatment solution applied to the surface of the aluminum material to thereby form a coating film, wherein: in the treatment solution to be applied to the surface of the aluminum material, a total of a concentration of the titanium fluoride compound in terms of titanium and a concentration of the zirconium fluoride compound in terms of zirconium is 20 to 400 ppm; and the application unit applies the treatment solution to the surface of the aluminum material so that a total of titanium and zirconium is 4 to 25 mg/m².

According to the surface treatment apparatus, since the application unit applies the treatment solution having the proper titanium concentration and the proper zirconium concentration, unreacted fluorine compounds derived from the treatment solution do not remain in the drying unit. Thus, the amount of fluorine compounds distributed in the surface of the coating film is reduced. Due to the reduction in the amount of fluorine compounds, the coating film can exert excellent bond durability. In addition, since the coating film is formed by applying the treatment solution in the application unit, the treatment solution which has reacted in the surface of the aluminum material or the coating film which has been formed on the surface does not have to be rinsed with water. Therefore, the treatment time of the surface treatment is shortened, and the quantity of waste liquid after rinsing the aluminum material with water is reduced. That is, the productivity or the environmental feasibility can be improved, and the energy cost can be also reduced. In addition, the application unit applies the treatment solution having the proper titanium concentration and the proper zirconium concentration while adjusting the total amount of applied titanium and zirconium. Thus, the coating film formed has a proper coating amount. Therefore, there is no fear that the coating amount is so small as to lose corrosion resistance or adhesion to a bonding agent, or there is no fear that the coating amount is so large as to make the coating film fragile. Combined with the reduction of fluorine compounds, the coating film can exert excellent bond durability. In addition, when the fluorine compounds eliminated in the drying unit can be surely disposed of by a scrubber or the like placed in the drying unit. Further, a water rinsing device does not have to be placed in a subsequent stage of the drying unit. It is therefore possible to easily obtain a miniaturized surface treatment apparatus high in environmental feasibility.

In the surface treatment apparatus of an aluminum material according to the present invention, it is preferable that the aluminum material is an aluminum sheet, and the surface treatment apparatus further includes a feeding unit that allows the aluminum sheet to pass through the application unit and the drying unit.

According to the surface treatment apparatus, the treatment capacity of the coating-type surface treatment is improved. Thus, the productivity is further improved.

A coating-type surface-treated aluminum material according to the present invention includes an aluminum material, and a coating film formed on a surface of the aluminum material and containing at least one kind of titanium and zirconium, and in the coating film, a total amount of a coating amount of titanium and a coating amount of zirconium is 3 to 17 mg/m², and a ratio (fluorine amount/sum of titanium amount and zirconium amount) of a fluorine amount in the surface to a sum of a titanium amount in the surface and a zirconium amount in the surface is 4.0 or less.

According to the surface-treated aluminum material, the coating film formed on the surface of the aluminum material has a predetermined coating amount of titanium and a predetermined coating amount of zirconium. Thus, the coating film can have excellent bond durability.

Advantageous Effects of the Invention

According to the surface treatment method and surface treatment apparatus in the present invention, a coating film having excellent bond durability can be formed on a surface of an aluminum material in spite of reduction in energy cost and environmental load. In addition, according to the surface-treated aluminum material in the present invention, a coating film can have excellent bond durability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of the steps in a surface treatment method according to the present invention.

FIG. 2 is a schematic view of a surface treatment apparatus for use in the surface treatment method according to the present invention.

FIG. 3 is a schematic sectional view illustrating a configuration of a surface-treated aluminum material according to the present invention.

FIG. 4 is a schematic view of a procedure of a bondability evaluating test for the surface-treated aluminum material.

DESCRIPTION OF EMBODIMENTS

Embodiments of a surface treatment method, a surface treatment apparatus and a surface-treated aluminum material according to the present invention are described. First, the surface treatment apparatus for use in the surface treatment method according to the present invention is described. As illustrated in FIG. 2, a surface treatment apparatus 21 includes a treatment solution application device (application unit) 11, a drying device (drying unit) 12, and feed rolls (feeding unit) 20. In the surface treatment apparatus 21, the treatment solution application device 11 and the drying device 12 are disposed adjacently to each other so that treatment by the drying device 12 can be performed next to treatment by the treatment solution application device 11. The respective constituents in the surface treatment apparatus 21 are described below.

(Treatment Solution Application Device)

The treatment solution application device 11 is a device that applies a treatment solution to a surface of an aluminum material 1. In the treatment solution application device 11, a treatment solution containing at least one kind of a titanium fluoride compound and a zirconium fluoride compound is applied to the surface of the aluminum material 1. The term “application” used here means an application operation for a coating type surface treatment. Differently from application for a reaction type surface treatment, the term “application” means, in the coating type surface treatment, an application operation in which a coating amount depending on an amount of the treatment solution applied to the surface of the aluminum material 1 can be obtained in a coating film after the coating film is dried. FIG. 2 shows a form using a coating method in which the treatment solution is applied onto the aluminum material 1. However, a device using a spray method in which the treatment solution is sprayed onto the aluminum material 1 to be thereby applied thereto or a device using an immersion method in which the aluminum material 1 is immersed into the treatment solution to be thereby applied thereto may be used as long as it is a device which can be used for the purpose of the coating type surface treatment. However, it is preferable that the treatment solution application device 11 is not accompanied with a water rinsing device for rinsing out unnecessary reaction products remaining after reaction of the treatment solution.

The treatment solution application device 11 may be any device as long as it can apply the treatment solution to the surface of the aluminum material 1. For example, the treatment solution application device 11 may be a roll coater as illustrated in FIG. 2, or may be any one of various coaters (coating machines) known in the background art, such as a bar coater or a die coater. When the treatment solution application device 11 is arranged as a device for performing a spray method, it may include a spray. When the treatment solution application device 11 is arranged as a device for performing an immersion method, it may include a treatment bath.

In detail, in the treatment solution applied by the treatment solution application device 11, a total of a concentration of the titanium fluoride compound in terms of titanium and a concentration of the zirconium fluoride compound in terms of zirconium is 20 to 400 ppm. The treatment solution application device 11 has to apply the treatment solution to the surface of the aluminum material 1 so that a total amount of applied titanium and zirconium is 4 to 25 mg/m². To this end, it is preferable that the treatment solution application device 11 is operated to apply the treatment solution at a coating amount of 20 to 100 mL/m². The concentrations in the treatment solution, the total amount of applied titanium and zirconium, and the amount of the applied treatment solution are explained specifically in the surface treatment method of the present invention which are described later.

(Drying Device)

The drying device 12 is a device which dries the aluminum material 1 fed from the treatment solution application device 11. In the drying device 12, the treatment solution applied to the surface of the aluminum material 1 by the treatment solution application device 11 is dried to form a coating film 2. The drying device 12 may be any device as long as it can perform a drying treatment for the aluminum material 1 to which the treatment solution has been applied. For example, the drying device 12 may be a device that performs a heating treatment (treatment temperature: 50 to 150° C. and treatment time: 10 to 60 seconds) on the applied treatment solution, or may be a device that sprays hot air or dried air to the applied treatment solution. In addition, a scrubber may be placed for disposing of eliminated fluorine compounds. In the aluminum material 1 treated in the drying device 12, the fluorine amount in the surface of the coating film 2 is reduced at the point of time when drying of the treatment solution is finished. Therefore, a water rinsing device for rinsing the formed coating film 2 with water does not have to be provided between the drying device 12 and a tension reel 13.

(Feed Rolls)

The feed rolls 20 feed the aluminum material 1 to the treatment solution application device 11 or the drying device 12. FIG. 2 shows a configuration (configuration for performing a surface treatment) in which an object to be treated in the treatment solution application device 11 or the drying device 12 is an aluminum sheet having a long belt-like shape, and each treatment is performed on the aluminum sheet which is being passed (moved) by the feed rolls 20. With this configuration, the treatment capacity can be improved to enhance the productivity of the aluminum material 1 (surface-treated aluminum material) having the coating film 2 formed on its surface.

In addition, in FIG. 2, the surface treatment apparatus 21 has a pay-off reel 10 and a tension reel 13. With this configuration, the aluminum sheet paid-off from the pay-off reel 10 is subjected to each treatment continuously in its lengthwise direction and taken up by the tension reel 13. Thus, the treatments performed on the aluminum sheet which is being passed by the feed rolls 20 are more efficient to improve the productivity. When the aluminum material 1 to be treated is, for example, shaped as a cast or extruded material, a conveyor or the like may be used in place of the feed rolls 20, and the pay-off reel 10 and the tension reel 13 do not have to be provided.

In the surface treatment apparatus 21, a degrease device and an acid pickling device known in the background art may be further provided at preceding stages of the treatment solution application device 11, and each of the degrease device and the acid pickling device may be accompanied with a water rinsing device (not shown). The degrease device or the acid pickling device is a device for removing an oil content remaining on the surface of the aluminum material 1 or an aluminum oxide coating film or magnesium oxide coating film formed on the surface.

Next, the surface treatment method according to the present invention is described with reference to the drawings.

As illustrated in FIG. 1, the surface treatment method according to the present invention includes a treatment solution application step S5 and a drying step S6. The surface treatment method according to the present invention may include a degrease step S1, a water rinsing step S2, an acid pickling step S3, and a water rinsing step S4 prior to the treatment solution application step S5. The respective steps are described specifically below. FIG. 3 is referred to as one example of the configuration of a surface-treated aluminum material obtained by the surface treatment method according to the present invention.

(Degrease Step)

The degrease step S1 is a step of washing the surface of the aluminum material 1 with an alkali to thereby remove an oil content remaining on the surface of the aluminum material 1. Here, the oil content may include lubricating oil attached to the surface of the aluminum material 1 when the aluminum material 1 is manufactured. A device known in the background art, which is provided in a carrying-in route of the aluminum material 1, or conditions known likewise may be used as the degrease device or degrease conditions. When the amount of the attached oil content remaining on the surface of the aluminum material 1 is negligible, the degrease step S1 may be omitted.

(Water Rinsing Step)

The water rinsing step S2 is a step of rinsing the surface of the aluminum material 1 with water to thereby remove the alkali remaining on the surface of the aluminum material 1. A device or conditions known in the background art may be used as the water rinsing device or water rinsing conditions. When the degrease step S1 is omitted, the water rinsing step S2 may be also omitted.

(Acid Pickling Step)

The acid pickling step S3 is a step of washing the surface of the aluminum material 1 with an acid to thereby remove an aluminum oxide coating film or a magnesium oxide coating film remaining on the surface of the aluminum material 1. Here, the aluminum oxide coating film and the magnesium oxide coating film are oxide coating films formed on the surface of the aluminum material 1 when the aluminum material 1 is manufactured. A device or conditions known in the background art may be used as the acid pickling device or acid pickling conditions. When the amount of the aluminum oxide coating film or magnesium oxide coating film remaining on the surface of the aluminum material 1 is negligible, the acid pickling step S3 may be omitted.

(Water Rinsing Step)

The water rinsing step S4 is a step of rinsing the surface of the aluminum material 1 with water to thereby remove the acid remaining on the surface of the aluminum material 1. A device or conditions known in the background art may be used as the water rinsing device or water rinsing conditions. When the acid pickling step S3 is omitted, the water rinsing step S4 may be also omitted.

(Treatment Solution Application Step)

The treatment solution application step S5 is a step of applying a treatment solution containing at least one kind of a titanium fluoride compound and a zirconium fluoride compound to the surface of the aluminum material 1. In the treatment solution application step S5, the treatment solution applied to the surface of the aluminum material 1 reacts with the aluminum material 1 to form the coating film 2 containing at least one kind of the titanium fluoride compound and the zirconium fluoride compound on the surface of the aluminum material 1. The application in the treatment solution application step S5 means a treatment operation for a coating type surface treatment. Differently from application for a reaction type surface treatment, the application in the treatment solution application step S5 means a treatment operation by which a coating amount depending on an amount of the treatment solution attached to the surface of the aluminum material 1 can be obtained in the coating film after the coating film is dried. The application in the treatment solution application step S5 may have any form of a coating method, a spraying method and an immersion method as long as it is a treatment operation for a coating type surface treatment. However, it is preferable that the application in the treatment solution application step S5 is not accompanied with a water rinsing step for rinsing out unnecessary reaction products remaining after reaction of the treatment solution.

Here, examples of such titanium fluoride compounds may include fluorotitanate such as K₂TiF₆ and (NH₄)₂TiF₆, fluorotitanate acid such as H₂TiF₆, and the like. Examples of such zirconium fluoride compounds may include fluorozirconate such as K₂ZrF₆ and (NH₄)₂ZrF₆, fluorozirconate acid such as H₂ZrF₆, and the like.

The coating film 2 containing at least one kind of titanium and zirconium is, for example, formed in the following series of reactions.

Al ↔ Al³⁺ + 3e⁻ Reaction Formula (I) O₂ + 2H₂O + 4e⁻ ↔ 4OH⁻ Reaction Formula (II) 2H⁺ + 2e⁻ ↔ H₂ Reaction Formula (III) Al³⁺ + TiF₆ ²⁻ ↔ AlF₆ ³⁻ + Ti⁴⁺ Reaction Formula (IV) Al³⁺ + ZrF₆ ²⁻ ↔ AlF₆ ³⁻ + Zr⁴⁺ Reaction Formula (V) Ti⁴⁺ + 3H₂O ↔ TiO₂•H₂O + 4H⁺ Reaction Formula (VI) Zr⁴⁺ + 3H₂O ↔ ZrO₂•H₂O + 4H⁺ Reaction Formula (VII)

In the treatment solution to be applied to the surface of the aluminum material 1, a total of a concentration of the titanium fluoride compound in terms of titanium and a concentration of the zirconium fluoride compound in terms of zirconium is 20 to 400 ppm. The phrases “in terms of titanium” and “in terms of zirconium” mean that the concentrations (mass/volume) of the compounds are converted into the concentrations of titanium atoms or zirconium atoms contained in the compounds, respectively. By use of the treatment solution having such concentrations, a total (g/m²) of titanium (in terms of metal titanium) and zirconium (in terms of metal zirconium) applied to the aluminum material 1, that is, an applied amount in terms of mass of metal atoms can be set within a range suitable for forming the coating film 2 when the treatment solution is applied within an applied amount range (20 to 100 mL/m²) described below. On the other hand, when the total of the concentrations in terms of mass of metal atoms is less than 20 ppm, a sufficient coating amount of the coating film 2 cannot be formed. On the contrary, when the total of the concentrations in terms of mass of metal atoms is more than 400 ppm, fluorine compounds such as hydrogen fluoride derived from the treatment solution are hardly eliminated. Thus, the amount of fluorine compounds in the surface of the coating film 2 increases to deteriorate the bond durability of the coating film 2.

The total of the concentration of the titanium fluoride compound and the concentration of the zirconium fluoride compound, in terms of metal atoms, may be 40 ppm or more, 80 ppm or more, or 120 ppm or more, for example, in order to increase the coating amount of the coating film 2. In addition, for example, in order to improve the bond durability, the total may be 360 ppm or less, 320 ppm or less, or 280 ppm or less.

The amount of the applied treatment solution to the to-be-applied surface of the aluminum material 1 is preferably 20 to 100 mL/m². When the amount of the applied treatment solution is less than 20 mL/m², it is necessary to set the treatment solution at a high concentration in order to form a proper coating amount of the coating film 2. However, when the concentration in the treatment solution is made too high, the amount of fluorine compounds generated in the surface of the coating film 2 increases to lower the bond durability of the coating film 2. On the contrary, when the amount of the applied treatment solution exceeds 100 mL/m², the reaction efficiency or uniformity of the coating film 2 deteriorates so that it is difficult to form the coating film 2 properly. The applied amount to the to-be-applied surface of the aluminum material 1 can be, for example, adjusted by increase or decrease in the amount of the treatment solution to be applied, the feeding rate of the aluminum material 1, or the like.

In detail, in the treatment solution application step S5, the treatment solution is applied to the surface of the aluminum material 1 so that a total of titanium and zirconium is 4 to 25 mg/m². The total amount is a sum of an amount in terms of metal titanium converted into mass of titanium atoms and an amount in terms of metal zirconium converted into mass of zirconium atoms. When the treatment solution having such a total amount is applied, the coating amount of the coating film 2 falls within a proper range after the titanium atoms or zirconium atoms contained in the treatment solution are dried to be partially evaporated and lost. On the other hand, when the total of titanium and zirconium is less than 4 mg/m², it is not possible to form a sufficient coating amount of the coating film 2. On the contrary, when the total of titanium and zirconium exceeds 25 mg/m², the coating amount of the coating film 2 is too large. Thus, the amount of fluorine compounds increases accordingly, so that the bond durability of the coating film 2 deteriorates.

The total of titanium and zirconium is more preferably 5 mg/m² or more, for example, in order to increase the coating amount of the coating film 2. When the total amount increases, the corrosion resistance or the bond durability is improved. In addition, the total of titanium and zirconium is more preferably 20 mg/m² or less, for example, in order to improve the bond durability. With such a total amount, the coating amount of the coating film 2 is not excessive, and the coating film 2 is hardly fragile. Thus, the coating film 2 is also prevented from being peeled off. In order to apply the treatment solution in which the total of titanium and zirconium has been adjusted, the concentrations in the treatment solution and the amount of the applied treatment solution to the to-be-applied surface of the aluminum material 1 may be increased or decreased.

(Drying Step)

The drying step S6 is a step of drying the treatment solution applied to the surface of the aluminum material 1 in the treatment solution application step S5 to thereby form the coating film 2. The drying treatment in the drying step S6 may be, for example, a treatment of heating the applied treatment solution (treatment temperature: 50 to 150° C. and treatment time: 10 to 60 seconds), or a treatment of spraying hot air or dried air to the applied treatment solution. In the aluminum material 1 treated in the drying step S6, the fluorine amount in the surface of the coating film 2 is reduced at the point of time when drying of the treatment solution is finished, as described later. Therefore, a surface-treated aluminum material having excellent bond durability can be obtained after the drying step S6 without performing a water rinsing step of rinsing the coating film 2 with water.

Next, the surface-treated aluminum material obtained by the surface treatment method according to the present invention is described. As illustrated in FIG. 3, the surface-treated aluminum material includes an aluminum material 1 and a coating film 2 formed on a surface of the aluminum material 1. Here, the surface of the aluminum material 1 means at least one surface of the aluminum material 1, and may include so-called one surface, two surfaces, or a plurality of surfaces.

The respective constituents are described below.

(Aluminum Material)

The aluminum material 1 is provided in a form of a sheet material having a coil-like shape or a sheet-like shape, or in a form of a cast or extruded material. Preferably the aluminum material 1 is provided as the sheet material. As for an aluminum alloy forming the aluminum material 1, an Al—Mg alloy or an Al—Mg—Si alloy is preferred. The Al—Mg alloy is a JIS-5000 series alloy, and the Al—Mg—Si alloy is a JIS-6000 series alloy.

The aluminum material 1 has a thickness of 0.7 to 3.0 mm. When the thickness is less than 0.7 mm, the strength is insufficient. When the thickness exceeds 3.0 mm, the manufacturing cost increases. The thickness of the aluminum material 1 is preferably 0.8 mm or more from the viewpoint of the strength, and preferably 2.3 mm or less from the viewpoint of the manufacturing cost.

(Coating Film)

The coating film 2 is a coating film containing a predetermined amount of titanium and zirconium. Titanium in the coating film 2 is preferably at least one of titanium oxide and titanium fluoride, and zirconium in the coating film 2 is preferably at least one of zirconium oxide and zirconium fluoride. In addition to titanium and zirconium, the coating film 2 is composed of a remainder of aluminum and impurities. Here, aluminum oxide, aluminum fluoride, or the like may be included as the aluminum as the remainder.

The total amount of the coating amount of titanium in terms of metal titanium and the coating amount of zirconium in terms of metal zirconium is 3 to 17 mg/m². It is preferable that the coating film 2 satisfies at least one of the conditions, that is, the condition that the coating amount of titanium is 1 to 10 mg/m² in terms of metal titanium and the condition that the coating amount of zirconium is 1 to 10 mg/m² in terms of metal zirconium. As a result, stability against deterioration factors such as water, oxygen, chloride ions, or the like increases to prevent hydration in the surface of the aluminum material 1 in a wet environment. In addition, the bond durability of the coating film 2 is improved.

When the total amount of the coating amount of titanium and the coating amount of zirconium in the coating film 2 is less than 3 mg/m², the effect of preventing hydration in the surface of the aluminum material 1 is insufficient. When the total amount exceeds 17 mg/m², breakage tends to occur inside the coating film when the aluminum material 1 is bonded. In addition, in order to prevent hydration in the surface of the aluminum material 1, the lower limit of the total amount of the coating amount of titanium and the coating amount of zirconium in the coating film 2 is preferably 5 mg/m². In order to prevent breakage inside the coating film when the aluminum material 1 is bonded, the upper limit of the total amount of the coating amount of titanium and the coating amount of zirconium in the coating film 2 is preferably 15 mg/m².

When the coating amount of titanium in the coating film 2 is less than 1 mg/m², the aforementioned effect is not obtained. When the coating amount of titanium exceeds 10 mg/m², the aforementioned effect is saturated to increase the manufacturing cost. In addition, breakage tends to occur inside the coating film when the aluminum material 1 is bonded. In order to prevent hydration in the surface of the aluminum material 1, the coating amount of titanium is preferably 2 mg/m² or more. On the other hand, in order to reduce the manufacturing cost of the coating film 2 and prevent breakage inside the coating film, the coating amount of titanium is preferably 8 mg/m² or less.

In addition, when the coating amount of zirconium in the coating film 2 is less than 1 mg/m², the aforementioned effect is not obtained. When the coating amount of zirconium exceeds 10 mg/m², the aforementioned effect is saturated to increase the manufacturing cost. In addition, breakage tends to occur inside the coating film when the aluminum material 1 is bonded. In order to prevent hydration in the surface of the aluminum material 1, the coating amount of zirconium is preferably 2 mg/m² or more. On the other hand, in order to reduce the manufacturing cost of the coating film 2 and prevent breakage inside the coating film, the coating amount of zirconium is preferably 8 mg/m² or less.

The thickness of the coating film 2 is not particularly limited as long as the coating amount of titanium and the coating amount of zirconium falls within the predetermined amounts, respectively. However, the thickness of the coating film 2 is preferably 10 to 150 nm. When the thickness of the coating film 2 is less than 10 nm, it is difficult to keep the bond durability. On the other hand, when the thickness of the coating film 2 exceeds 150 nm, the bond durability is saturated to increase the manufacturing cost.

A ratio (fluorine amount/sum of titanium amount and zirconium amount) of an “amount in terms of fluorine (fluorine amount)” to a “sum of an amount in terms of metal titanium (titanium amount) and an amount in terms of metal zirconium (zirconium amount)” in the surface of the coating film 2 is 4.0 or less. The value of the ratio is referred to as “surface F/(Ti+Zr)” below. The coating film 2 which has been formed by the drying treatment but has not been rinsed with water yet takes such a value of the surface F/(Ti+Zr). The concentrations in the treatment solution are set to be low and the amount of the applied treatment solution is adjusted so that the amount of fluorine compounds in the surface of the coating film 2 can be reduced. Since the amount of fluorine compounds is reduced, the coating film 2 has excellent bond durability.

When the surface F/(Ti+Zr) of the coating film 2 exceeds 4.0, the amount of fluorine compounds in the surface of the coating film 2 is so large that the bonding strength of the aluminum material 1 to another material such as an iron material is lowered, and the bond durability also deteriorates. In addition, a bonding agent which bonds the aluminum material 1 with the other material tends to be peeled off. Thus, it is unfavorably difficult to keep the bonding state particularly under a wet environment. In order to improve the bond durability or the like, the surface F/(Ti+Zr) of the coating film 2 is preferably 3.0 or less, more preferably 2.5 or less, and further more preferably 2.0 or less.

The surface F/(Ti+Zr) of the coating film 2 can be adjusted by increase or decrease in the concentration of the titanium fluoride compound or zirconium fluoride compound in the treatment solution. In addition, the surface F/(Ti+Zr) can be obtained by XPS (X-ray Photoelectron Spectroscopy) for measuring atom concentration distributions of an amount in terms of fluorine, an amount in terms of metal titanium and an amount in terms of metal zirconium. As for measuring conditions of the XPS, measuring can be performed under the conditions that aluminum Kα is used as a radiation source, data acquisition time (Dwell) is 100 ms, pass energy (pass) is 30 eV, and etching is absent. The amounts in terms of the respective elements can be determined based on their peak intensities, respectively.

The coating amount of titanium and the coating amount of zirconium in the coating film 2 can be measured by XRF (X-ray Fluorescence Analysis). In addition, the thickness of the coating film 2 can be measured by GD-OES (Glow Discharge Optical Emission Spectroscopy). In addition, the measuring method of the coating amount or the thickness is not limited to the XRF or the GD-OES, but any measuring method may be used as long as it has the same accuracy as the aforementioned measuring method.

Examples

Next, the surface treatment method and the surface-treated aluminum material according to the present invention are described specifically by comparison between Examples satisfying the requirements of the present invention and Comparative Examples not satisfying the requirements of the present invention.

First, an aluminum sheet having a width of 150 mm, a length of 200 mm and a thickness of 1.0 mm was produced using a JIS-6016 series alloy. The aluminum sheet was degreased with alkali, rinsed with water, then washed with acid and rinsed with water.

Respective amounts of applied treatment solutions (25° C.) having concentrations shown in Table 1 were applied to surfaces of aluminum sheets which had been washed with acid and then rinsed with water. After that, a drying treatment at 110° C. for 30 seconds was carried out to produce coating-type surface-treated aluminum sheets (No. 1 to No. 11).

A treatment solution (50° C.) containing 150 ppm of fluorotitanate as the titanium fluoride compound and 250 ppm of fluorozironate as the zirconium fluoride compound was sprayed for 3 seconds to a surface of an aluminum sheet which had been washed with acid and then rinsed with water. After that, a water rinsing treatment with water at 25° C. for 60 seconds was carried out, and drying at room temperature was then carried out to produce a reaction-type surface-treated aluminum sheet (No. 12).

In each of the coating films formed on the surfaces of the produced surface-treated aluminum materials (No. 1 to No. 12), the coating amount of titanium and the coating amount of zirconium were measured by the XRF (X-ray Fluorescence Analysis). The coating amounts in the surface-treated aluminum material were obtained by measuring one sheet chosen at random from a plurality of surface-treated aluminum materials treated under the same conditions. Measuring positions in each sheet were set in a total of five circular regions each having a diameter of 30 mm in the surface measuring 150 mm in width by 200 mm in length. The circular regions include four circular regions around points 50 mm inside on the diagonal lines from the four corners respectively, and one circular region around the center of the sheet. The coating amount of the surface-treated aluminum material was obtained as an average value of measured values in the five regions. In addition, the atom concentrations of the amount in terms of fluorine, the amount in terms of metal titanium and the amount in terms of metal zirconium in the surface of the coating film formed on the surface of each of the produced surface-treated aluminum materials (No. 1 to No. 12) were measured by the XPS (X-ray Photoelectron Spectroscopy). Thus, the surface F/(Ti+Zr) was calculated. The surface F/(Ti+Zr) of the surface-treated aluminum material was obtained by measuring one sheet chosen at random from a plurality of surface-treated aluminum materials treated under the same conditions, in the same manner. Measuring positions in each sheet were set in a total of five square regions each 1 mm square in the surface measuring 150 mm in width by 200 mm in length. The square regions include square regions located at the four corners and the center of the sheet. The surface F/(Ti+Zr) of the surface-treated aluminum material was obtained as an average value of measured values in the five regions.

Next, bonding test specimens 34 each having a lower test piece 31 and an upper test piece 33 bonded thereto through a bonding agent 32 as shown in FIG. 4 were produced using the surface-treated aluminum materials (No. 1 to No. 12), respectively. The following bond durability test was performed on the bonding test specimens 34. Specifically, the bonding test specimens 34 were produced in the following production method.

As illustrated in FIG. 4, the lower test piece 31 and the upper test piece 33 were put on top of each other and laminated by the thermosetting epoxy resin bonding agent 32 so as to have a lap length of 10 mm (bonding area: 25 mm by 10 mm). On this occasion, glass beads (particle size: 250 μm) were added to the bonding agent 32 to adjust the thickness of the bonding agent 32 to 250 μm. After that, they were burnt and hardened at 170° C. for 20 minutes. They were then left to stay at room temperature for 24 hours to obtain the bonding test specimen 34.

(Bond Durability Test)

Each bonding test specimen 34 produced was retained in spray of neutral salt water for 14 days. After that, unbonded portions of the lower and upper test pieces 31 and 33 were gripped and a shear tensile test at a rate of 10 mm/min was performed thereon. Autograph AG-50kNI manufactured by Shimadzu Corporation was used for the tensile test. Observation of a broken form of the bonding test specimen 34 and calculation of shear strength thereof were performed in the following procedure, and bond durability thereof was evaluated. Three bonding test specimens 34 were produced for each example, and an average value of the three was used as each of a cohesive failure ratio and shear strength shown below.

(Bond Durability Test: Fracture)

The peeling-off state of each bonding test specimen 34 after the tensile test was observed. Breakage inside the bonding agent 32 was regarded as cohesive failure, and peeling off in the interface between the lower test piece 31 and the bonding agent 32 or in the interface between the upper test piece 33 and the bonding agent 32 was regarded as interface breakage. The cohesive failure ratio was calculated as an index of the breakage form based on the following expression (1).

Cohesive failure ratio (%)=100−{(area of interface peeling in lower test piece 31/area of bonding in the lower test piece 31)×100+(area of interface peeling in upper test piece 33/area of bonding in the upper test piece 33)×100)}  (1)

In addition, the breakage form was evaluated by the following criterion: it was evaluated as not good “x” when the cohesive failure ratio was less than 90%, and as good “o” when the cohesive failure ratio was 90% or more.

(Bond Durability Test: Shear Strength)

The maximum stress at breakage was obtained from a stress-strain diagram obtained in the tensile test, and was regarded as shear strength.

The following Table 1 shows, for each example, a method used for surface treatment, concentrations in terms of titanium and in terms of zirconium in the treatment solution applied to the surface of the aluminum sheet, the amount of the applied treatment solution, the coating weight of dry film, the result of the surface F/(Ti+Zr), the result of the evaluation about the fracture, and the result of the shear strength.

TABLE 1 Amount of Evaluation of Concentration in applied Coating weight Coating weight bondability treatment solution treatment of wet film of dry film Shear Treatment (ppm) solution (mg/m²) (mg/m²) Surface F/ strength No. method Ti Zr Total (mL/m²) Ti Zr Total Ti Zr Total (Ti + Zr) Fracture (MPa) 1 Coating type 200 200 400 20 4 4 8 4 3 7 2.7 ∘ 18.5 2 Coating type 100 100 200 40 4 4 8 3 2 5 1.9 ∘ 19 3 Coating type 40 40  80 100 4 4 8 2 3 5 1.8 ∘ 19.4 4 Coating type 120 120 240 100 12 12 24  7 8 15  1.9 ∘ 18.7 5 Coating type 60 60 120 40 2.4 2.4   4.8 2 2 4 2.1 ∘ 19.4 6 Coating type 200 0 200 40 8 0 8 7 0 7 1.8 ∘ 19.3 7 Coating type 0 200 200 40 0 8 8 0 7 7 1.8 ∘ 19.3 8 Coating type 240 240 480 15 3.6 3.6   7.2 3 3 6 5.9 x 17.6 9 Coating type 400 400 800 10 4 4 8 4 3 7 6.5 x 16.1 10 Coating type 150 150 300 100 15 15 30  10 10 20  2.6 x 16.8 11 Coating type 40 40  80 40 1.6 1.6   3.2 1 1 2 1.3 x 17.2 12 Reaction type — — — — — — — 4 4 8 0.7 ∘ 19.6

As shown in Table 1, in the surface-treated aluminum material in No. 12 taken as a reference example, a coating film was formed by reaction-type surface treatment, and subjected to water rinsing treatment. Thus, the value of “surface F/(Ti+Zr)” was low. Therefore, the shear strength was high, and a fracture was hardly caused by peeling off. Thus, the coating film had excellent bond durability.

On the other hand, in the coating-type surface-treated aluminum material in each of No. 1 to 7 where the coating film was formed by the coating type surface treatment, the concentrations in the applied treatment solution and the amount of the applied treatment solution were within the proper ranges. Thus, the value of “surface F/(Ti+Zr)” was controlled to be small. The coating film was formed by the coating type surface treatment, but not subjected to water rinsing treatment. Notwithstanding, the shear strength is as high as that of the reaction-type surface-treated aluminum material in No. 12 subjected to water rinsing treatment. Therefore, a fracture was hardly caused by peeling off, and the coating film had excellent bond durability.

On the other hand, in the coating-type surface-treated aluminum material in each of No. 8 and 9, the concentrations in the applied treatment solution were out of the proper ranges. Since the concentrations were too high, the value of “surface F/(Ti+Zr) was high. Therefore, the shear strength was so low that a fracture tended to be caused by peeling off. Thus, the bond durability of the coating film was not improved.

Further, in the coating-type surface-treated aluminum material in each of No. 10 and 11, the amount of the applied treatment solution was out of the proper range. Since the coating film did not have a proper coating amount, the coating film was fragile in spite of a low value of “surface F/(Ti+Zr). Therefore, the shear strength was so low that a fracture tended to be caused by peeling off. Thus, the bond durability of the coating film was not improved.

The embodiments and the examples have been described above in detail about the surface treatment method, the surface treatment apparatus and the surface-treated aluminum material according to the present invention. However, the gist of the present invention is not limited to the aforementioned contents. The scope of rights of the present invention should be interpreted based on description of the scope of claims. It is a matter of course that the contents of the present invention can be modified or changed based on the aforementioned statement.

The present application is based on Japanese patent application No. 2016-066564 filed on Mar. 29, 2016, and Japanese patent application No. 2016-231695 filed on Nov. 29, 2016, the contents of which are incorporated herein by reference.

INDUSTRIAL APPLICABILITY

The aluminum material according to the present invention has a coating film with excellent bond durability in spite of reduction in energy cost and environmental load. It is useful in transportation equipment such as an automobile, a ship, or an airplane, particularly for an automobile panel

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS

-   -   S1 Degrease step     -   S2 Water rinsing step     -   S3 Acid pickling step     -   S4 Water rinsing step     -   S5 Treatment solution application step     -   S6 Drying step     -   1 Aluminum material     -   2 Coating film     -   3 Surface-treated aluminum material     -   11 Treatment solution application device     -   12 Drying device     -   21 Surface treatment apparatus     -   31 Lower test piece     -   32 Bonding agent     -   33 Upper test piece     -   34 Bonding test specimen 

1. A surface treatment method of an aluminum material, comprising the steps of: applying a treatment solution containing at least one kind of a titanium fluoride compound and a zirconium fluoride compound to a surface of an aluminum material; and drying the treatment solution applied to the surface of the aluminum material, thereby forming a coating film, wherein: in the treatment solution to be applied to the surface of the aluminum material, a total of a concentration of the titanium fluoride compound in terms of titanium and a concentration of the zirconium fluoride compound in terms of zirconium is 20 to 400 ppm; and the treatment solution is applied to the surface of the aluminum material so that a total of titanium and zirconium is 4 to 25 mg/m².
 2. A surface treatment apparatus of an aluminum material, comprising: an application unit that applies a treatment solution containing at least one kind of a titanium fluoride compound and a zirconium fluoride compound to a surface of an aluminum material; and a drying unit that dries the treatment solution applied to the surface of the aluminum material to thereby form a coating film, wherein: in the treatment solution to be applied to the surface of the aluminum material, a total of a concentration of the titanium fluoride compound in terms of titanium and a concentration of the zirconium fluoride compound in terms of zirconium is 20 to 400 ppm; and in the application unit, the treatment solution is applied to the surface of the aluminum material so that a total of titanium and zirconium is 4 to 25 mg/m².
 3. The surface treatment apparatus of an aluminum material according to claim 2, wherein: the aluminum material is an aluminum sheet; and the surface treatment apparatus further comprises a feeding unit that allows the aluminum sheet to pass through the application unit and the drying unit.
 4. A coating-type surface-treated aluminum material comprising an aluminum material, and a coating film formed on a surface of the aluminum material, the coating film containing at least one kind of titanium and zirconium, wherein, in the coating film, a total amount of a coating amount of titanium and a coating amount of zirconium is 3 to 17 mg/m², and a ratio (fluorine amount/sum of titanium amount and zirconium amount) of a fluorine amount in the surface to a sum of a titanium amount in the surface and a zirconium amount in the surface is 4.0 or less. 